Atherosclerotic thickenings of blood vessel walls occur in humans and animals. These thickenings are composed of cells and accumulated lipid. Because of the importance of cells in atherogenesis, cell suspensions prepared from human and animal atheroscelerotic lesions are being characterized using a new technology, flow cytometry and sorting. Flow cytometry is a technique in which measurements of light scatter (indicating cell size and structure) and fluorescence emission are simultaneously carried out on fluorescently stained cells as they flow in suspension one at a time past a laser. Sepecified cell populations may be purified by causing droplets containing desired cells to be deflected into a collection reservoir. Dissociation of human and animal atherosclerotic vessels has been carried out using mild homogenization and enzymatic digestion respectively. Different cell types are present in homogenates prepared from lesions. Light scatter and fluorescene analyses of these dissociated cells are being carried out